Indeed. There is a lot on this thread based on Argument from Silence.
The Catholics want to prove that Mary was a perpetual virgin, they most likely believe it or they would not try to prove it
The protestants want to prove the Catholics wrong so as to say you can not be the successors of Peter other wise how could you be so wrong?
Both sides uses assumptions which proves nothing.
And I agree it has nothing to do with salvation, Jesus said “I am the way and the truth and the life” (John 14:6), not his mother, his brothers or half brothers or step brothers or sisters.
Mathew 4
4 Who answered and said: It is written, Not in bread alone doth man live, but in every word that proceedeth from the mouth of God.
What Jesus said came from God and is the final word.
Some of the thing Jesus said are hard to understand but the things he plainly told us to do are fairly simple.
I agree with you that salvation doesn't require belief in Peter as Pope nor a belief in the perpetual virginity of Mary. However, Roman Catholics wouldn't agree, at least in my understanding. Can a Roman Catholic tell us for sure: is denial of the belief in Mary's perpetual virginity a mortal sin?